The present invention relates to an electroacoustic transducer, especially to an electroacoustic transducer having a slender diaphragm.
Much attention has been given to slender-type electroacoustic transducers that exhibit high space saveability and excellent audio characteristics, for use in TVs, speakers in surround systems.
The applicant of the present invention has proposed such a slender-type electroacoustic transducer, which will also be referred to as an SPU (Speaker Unit) hereinafter, in documents, for example, Japanese Unexamined Patent Publications Nos. 2002-325294 and 2004-297315 (referred to as Document 1 and 2, respectively, hereinafter).
Document 1 discloses an electroacoustic transducer equipped with a track-like diaphragm supported by a rectangular frame via an edge member formed around the diaphragm and attached to the frame. As shown in FIGS. 1 and 4, the edge member is formed into a flat ring shape and attached to the frame at its outer periphery. In another word, the frame is the outermost member of the electroacoustic transducer in the transversal (width) direction.
In the description below, the structure of a diaphragm with an edge member formed therearound is referred to as a diaphragm assembly.
The market demands for slender speaker units with wider frequency characteristics. In order to meet the demand, the applicant proposes a “slim-type” electroacoustic transducer in Document 2. As shown in FIGS. 1 and 2, the slim type has a flange folded at its side section lying along the longitudinal section of the edge member and fixed to the outer surface of a frame. In another word, the edge member (flange) is the outermost member of the electroacoustic transducer in the transversal direction within a zone including at least a diaphragm.
Compared to the electroacoustic transducer in Document 1, the slim type is much narrower in the transversal direction with its flange folded at the side section and fixed to the frame even though the diaphragm of the slim type is formed as having the same width as that in Document 1. For example, when the width of the electroacoustic transducer in Document 1 is 30 mm, the slim type in Document 2 can be formed as having the width of 22 mm even though the diaphragm has the same width in both transducers.
In another word, the slim type can be formed as having the same width for the diaphragm as that of Document 1 even though the width of the transducer is made narrower than that of Document 1. The slim type thus maintains comparatively wide linear response range for the diaphragm to a driving force applied thereto.
The electroacoustic transducers in Document 1 and 2 are both produced such that the yoke and the frame are boned to each other at their side sections at the longitudinal (length) direction, and almost sealed except for the end sections of the diaphragm in the rear side in the transversal (width) direction.
In spite of the advantages of the slim-type electroacoustic transducer discussed above, the inventor of the present invention found several disadvantages listed below, when trying to achieve wider frequency range in reproduction of low sounds and higher efficiency, and also to improve input characteristics to larger inputs, with a wider diaphragm.
(1) A wider diaphragm causes a low ridigity to the diaphragm assembly of the diaphragm with the edge member, resulting in poor frequency characteristics.
(2) A wider diaphragm causes that the diaphragm supporting and driving mechanisms become weaker physically to the wider diaphragm, resulting in unstable vibration of the diaphragm at larger strokes.
(3) A wider diaphragm causes excess heat from the voice coil when a large drive current is applied, resulting in a break in the coil windings, thermal degradation of the adhesive or the peripheral members of the voice coil, etc., with shorter life and poor aging reliability.
(4) A wider diaphragm causes an excess pressure to the rear side of the diaphragm when it vibrates at a large stroke because the diaphragm is almost sealed except for the end sections of the diaphragm in the rear side in the transversal direction, resulting in aerodynamic noises easily generated from the gap formed in the diaphragm assembly.
(5) A wider diaphragm causes a larger swing to a pair of lead wires of the diaphragm when it vibrates at a larger stroke, which further causes that lead wires touch each other so that it may cause a short between the wires, resulting in lower reliability.
Besides the problems of the wider diaphragm discussed above, the slim-type electroacoustic transducer has another problem. A problem could occur when this type of transducers are piled each other, for shipment, with the diaphragm assembly of the diaphragm and the edge member attached to the diaphragm. In detail, the members that vibrate when driven, such as, the diaphragm and the rolled section of the edge member, could touch each other when the transducers are piled and thus could be damaged or deformed.